Cetylpyridinium chloride is a cationic bactericide useful for inhibiting formation of dental plaque and it has hitherto been proposed to add it to dentifrices. However, since ingredients used in conventional dentifrices such as foaming agents and the like are normally anionic, cetylpyridinium chloride reacts with them, which results in a loss of its bactericidal activity. Accordingly, when it is used, measures for stabilizing cetylpyridinium chloride should be taken.
Under these circumstances, the present inventors have studied to stably formulate cetylpyridinium in a dentifrice. As a result, it has been found that an aqueous gel comprising a polyoxyethylene-polyoxypropylene block copolymer surfactant has desired properties as a dentifrice, and can specifically stabilize cetylpyridinium chloride.
An aqueous gel comprising a polyoxyethylene-polyoxypropylene block copolymer surfactant is disclosed in U.S. Pat. No. 3,740,421 for using in various fields such as cosmetics and drugs, and has been already known. However, such an aqueous gel has a problem that phase transition from gel to sol is caused at a low temperature, which results in a lowering of viscosity, as disclosed in International Journal of Pharmaceutics, 39 (1987), pages 121 to 127. Accordingly, when such an aqueous gel is used for the preparation of a dentifrice composition, there are problems such as deterioration of shape retention at a low temperature due to a lowering of viscosity, impairment of feeling of use, and solid-liquid separation due to sedimentation of a polishing agent, which makes the preparation of the dentifrice composition difficult.